Research invented and patented at DTU Fotonik is appearing in the advance online issue of Nature Methods.
The upcoming Nature Methods features a report describing pioneering laser research that will be of tremendous value for biophotonics scientists and neuro-photonics specialists in the future. The work has been performed by the groups of Valentina Emiliani at Paris Descartes University in Paris, Ehud Isacoff at UC Berkeley and Lawrence Berkeley National Lab. in California and by Jesper Glückstad from the Dynamic Photonics cluster at DTU Fotonik.
The paper presents a powerful approach for controlling light-gated ion channels and pumps that makes it possible to probe intact neural circuits by manipulating the activity of groups of genetically similar neurons. It is experimentally demonstrated how it is now possible to precisely aiming stimulating light at single neuronal processes, neurons or groups of neurons. The underlying laser technique combines Jesper Glückstad´s patented Generalized Phase Contrast (GPC) with socalled temporal focusing to shape two-photon excitation for this purpose. The laser excitation patterns are generated automatically from fluorescence images of neurons and shaped to cover the cell body or dendrites, or distributed groups of cells. The temporal focusing GPC two-photon excitation patterns can generate large photocurrents in Channelrhodopsin-2–expressing cultured cells and neurons and in mouse acute cortical slices. The amplitudes of the photocurrents can be precisely modulated by controlling the size and shape of the excitation volume and, thereby, be used to trigger single action potentials or trains of action potentials.
The collaboration between Jesper Glückstad, Valentina Emiliani and Ehud Isacoff began a few years ago and was mainly triggered by the French groups desire to demonstrate a powerful femtosecond laser technique that would have the the ability to rapidly and automatically create two-photon excitation shapes for simultaneous excitation of multiple cells and cell processes in a highly precise way and only adressing a particular layer of cells in a slice. The GPC method coupled with temporal focusing turned out to be the "light engine" that was needed to achieve this pioneering demonstration and a complete laser setup was established in Paris to undertake the experimental demonstrations reported in this Nature Methods paper. The link to the advance online publication can be found here: http://www.nature.com/nmeth/journal/vaop/ncurrent/abs/nmeth.1505.html